FR3052440A1 - INTEGRATING A PHASE CHANGE MATERIAL TO LIMIT THE FUEL TEMPERATURE FROM AN ELECTRONIC MODULE. - Google Patents

Abstract

The invention relates to an assembly comprising: a fuel supply circuit (15, 15a, 15b) configured to supply a fuel turbine engine, an electronic module (14, 14a, 14b), a power source ( 13, 13a, 13b) for providing the electronic module (14, 14a, 14b) with electricity, a heat exchanger (16, 16a, 16b) positioned to allow heat flow of the electronic module (14, 14a, 14b) to the fuel supply circuit (15, 15a, 15b), the assembly being characterized in that the electronic module (14, 14a, 14b) comprises a phase change material (PCM), configured to change state when its temperature reaches a predetermined temperature of phase change (Tf).

Description

Integration of a phase change material to limit the temperature of the fuel from an electronic module

GENERAL TECHNICAL FIELD The invention relates to the feeding of a motor unit with fuel, and in particular, the management of the phase state of the fuel.

More specifically, the invention relates to power units comprising a heat engine and an electric machine.

The term "turbine engine" in the present context, any machine for converting the thermal energy of a working fluid into mechanical energy by expansion of said working fluid in a turbine.

More particularly, this working fluid can be a combustion gas resulting from the chemical reaction of a fuel with air in a combustion chamber, after the compression of this air in a compressor driven by the turbine through a first rotating shaft.

Thus, turbine engines, as understood in this context, include single or dual flow turbofan engines, turboprops, turboshaft engines or gas turbines, among others.

In the following description, the terms "upstream" and "downstream" are defined with respect to the normal flow direction of the working fluid in the turbomachine.

The fuel supplying turbine engines can include impurities, and in particular water in suspension. At normal temperatures the presence of traces of water in the fuel is not very problematic. However, when temperatures are low, this water may freeze. The resulting ice particles may possibly block the passage of the fuel, in particular by agglomerating at the inlet of the filters typically used to prevent the passage of other solid impurities. Therefore, this icing should be avoided in the fuel system.

STATE OF THE ART

A first solution against the freezing of fuel is to add additives, expensive, toxic and binding. This solution is deliberately discarded.

A second solution consists, as presented in document US 20120240593, in recovering the heat generated by an electronic circuit, in this case a power conversion electronic circuit (GCU for "Generator Control Unit"), for heating the fuel and preventing that the latter does not freeze. A heat exchanger makes it possible to carry out the heat transfers.

The GCU then functions as a radiator.

In the aforementioned document, the heat transfer management between the GCU and the fuel is done by controlling the fluid flow, or by adding an additional dedicated electric radiator, which allows on the one hand to generate additional heat and to solicit more the GCU, which in turn heats more. Nevertheless, there is a risk, not mentioned in the aforementioned document, that the fuel receives too much energy and can reach its vaporization temperature. Indeed, some embedded electronics operate for very short periods, which implies a high power. In addition, the voltage used, often of the order of a few tens of volts, causes very high amperages, resulting in significant heat generation.

This phenomenon of vaporization must be avoided.

PRESENTATION OF THE INVENTION The invention aims to remedy the aforementioned drawbacks by proposing an assembly comprising:

A fuel supply circuit configured to supply a fuel turbine engine,

An electronic module,

A source of energy to supply the electronic module with electricity,

A heat exchanger positioned to allow heat flow from the electronic module to the fuel supply circuit, the assembly being characterized in that the electronic module comprises a phase change material (PCM) configured to change state when its temperature reaches a predetermined phase change temperature.

Thanks to the PCM material, the temperature rise is better diffused over time, which makes it possible to limit the temperature peaks and thus to avoid reaching the vaporization temperature of the gasoline.

In addition, the PCM material protects the electronic module from these temperature peaks that can damage it.

The PCM material thus makes it possible to distribute the heat flow in an optimized manner between the electronic module and the fuel.

In order to prevent the fuel from vaporizing, the phase change temperature of the PCM material is chosen to be lower than the vaporization temperature of said fuel flowing in the fuel supply circuit. The invention may comprise the following characteristics, taken alone or in combination: said predetermined phase change temperature is lower than the vaporization temperature of the fuel, the electronic module is an electronic power module, configured to convert the energy provided by the energy source, the phase change temperature is less than 150 ° C, preferably less than 140 ° C. the electronic module comprises the following elements: a base substrate forming a support, electronic components positioned on the support, and in which the exchanger is located, with respect to the base substrate, on the side opposite to the components; electronic components are encapsulated in PCM phase change material, - PCM phase change material is integrated with the base substrate, - the electronic module comprises a cold plate, and in which phase change material is integrated into the cold plate. the cold plate is positioned between the base substrate and the heat exchanger, the heat exchanger is integrated with the cold plate, the invention also proposes a motor unit comprising:

A turbine engine,

An assembly as described above, wherein the fuel supply circuit is configured to supply the engine.

The energy source is advantageously an electric machine that can operate as a motor or generator and wherein the electric machine is mechanically coupled to a rotating shaft of the engine. The invention also proposes a method of heating fuel using an assembly or a power unit as described above, in which the fuel is heated, in the heat exchanger of the fuel supply circuit. by the heat emitted by the electronic module through the PCM phase change material. The invention also proposes the use of PCM phase change material for controlling the heat transfer between on the one hand an electronic module releasing heat when it is supplied with energy, and on the other hand a turbine fuel for gas, through a heat exchanger.

PRESENTATION OF THE FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the accompanying drawings, in which: FIG. 1 schematically illustrates a power electronics module and a motor group heat exchanger, shown without PCM material for the sake of clarity; - Figure 2 is similar to Figure 1, but with three PCM material integration variants, and with an addition of a cold plate, - Figure 3 shows temperature curves relating to the use of PCM material, - Figure 4 schematically illustrates an aircraft with a power unit comprising two turbine engines and two electric motors-generators, - the Figure 5 illustrates more specifically this motor group.

DETAILED DESCRIPTION

With reference to FIG. 1, an assembly is defined comprising a fuel supply circuit 15, an electronic module 14 and a power source 13 that supplies energy, typically electricity, to the module 14.

The fuel supply circuit 15 serves to supply a fuel turbine engine with fuel. Specific embodiments will be detailed later.

The electronic module 14 generally comprises at least one electronic circuit on which are connected together electronic components able to process electrical signals (information or energy).

Therefore, when it is biased by the power source 13, the module 14 emits heat. In order for this heat to be transmitted to the fuel supply circuit 15, a heat exchanger 16 is provided. Typically, the heat exchanger 16 is positioned between the electronic module 14 and the fuel supply circuit 15a, 15b. The heat exchanger 16 optimizes the heat flow between the module 14 and the supply circuit 15. It can take various forms, such as a plate heat exchanger, with fins, or simply in the form of ramifications of pipes promoting the heat exchange.

The electronic module 14 comprises in one embodiment a base substrate 100 forming a support on which are fixed electronic components 110, such as insulated gate bipolar transistors, diodes, capacitors, inductors, etc. As shown in FIG. 1, these components 110 may require emitters 112, gates 114, a collector 116 and connection wires 118 for example.

Different layers of materials, such as a brazed joint 102, a copper soleplate 104, another insulating substrate 106, for example ceramic, to make interconnections between the semiconductors and with external circuits on the copper soleplate 104 , are conventionally provided for the operation of the electronic module.

In order to better regulate the transfer of energy, the electronic module 14 comprises a phase-change material, referenced PCM for "phase-change material". Figure 2 shows various detailed embodiments thereafter.

PCM materials change state, usually from the solid state to the liquid state, as soon as their melting point is reached. Since there are also PCM materials that change phase from a solid or liquid state to a gaseous state, it is more generally referred to as a phase change temperature Tf.

This temperature Tf is a characteristic of the PCM material.

In certain flight phases of an aircraft, the electric power demand of an electrical system can be very high over times that do not exceed a few tens of seconds or even a minute. Under these conditions where a large heat dissipation is required but which is cyclic or transient, the use of PCM materials allows a better management of the thermal closer to the critical electronic components 110 such as the static components, capacitors, self, etc.

Indeed, reaching its melting temperature, thus passing from the solid state to the liquid state, the PCM material will absorb a quantity of heat while remaining at the same temperature (the time that the entire material has changed state). ) and heat transfer will then occur between the electronic components 110 inside the electronic module 14 and PCM material. This absorption is related to the enthalpy of change of state of the PCM material, also called latent heat, which corresponds to the energy that must receive a unit of mass of the material to change state.

The PCM material will then absorb the peak temperature.

Indeed, one of the main problems in the development of electronics on board aircraft is that of the temperature resistance of the electronic components 110, especially those which are brazed / soldered on the substrate 100. Indeed, the thermomechanical stresses between the component 110 and the substrate 100 may in some cases cause delamination of the solder or solder component on its substrate, which can destroy the component. Such uses of PCM material are already known, as in US 20130147050.

PCM material also allows for sizing and occupied volume gains. Indeed, the electronic components 110 such as transistors, capacitors, chokes, can be sized not on a peak peak temperature but on a lower average temperature.

Therefore, the PCM material has a primary role, which is to absorb heat to prevent the electronic module 14 from exceeding a critical temperature. FIG. 3 illustrates this absorption as a function of time: the curve C 0 represents the temperature rise of the electronic module 14 in the absence of PCM material, the curves C 1 to C 18 represent the temperature rise of the electronic module 14 in the presence of PCM material for different thermal resistances between the PCM material and the substrate 100, the curves C23 to C27 represent the temperature rise of the PCM material (in connection with the curves C13 to C17). Note that the phase change temperature Tf of the PCM material is slightly less than 120 ° C. However, as indicated above, the electronic module 14 also has the function of heating the fuel. However, it turns out that power peaks can generate too much heat and that the management of heat transfer is problematic.

As a result, the PCM material, which has absorbed the heat peak, progressively restores it to the exchanger 16a, 16b. Thus, the PCM material makes it possible to average the heat transfer between the electronic module 14 and the fuel.

In this way, the risks of vaporization of said fuel are greatly reduced. The integration of a PCM material in such a heat exchange architecture between the electronic module 14 and the fuel circuit 15 makes it possible to put a thermal barrier which, by diffusing the heat over time, protects the fuel from vaporization, while protecting the module 14 from overheating. In addition, contrary to conventional uses of PCM materials whose purpose is simply to absorb heat during a relatively short period of time, the PCM material is here used as a radiator, from the energy stored via the electronic module 14 .

In order for this function to be fulfilled, a PCM material whose phase change temperature Tf is lower than the vaporization temperature Tv of the fuel is chosen.

The following fuels are known, with their typical start vaporization temperature Tv indicated in parentheses: JetA (180 ° C), JP8 and JP8 + 100 (170 ° C), JetAl (170 ° C), JP5 (200 ° C) , F76 (200 ° C), TS1 (160 ° C) and RT (160 ° C).

For these fuels, a temperature Tf of less than 150 ° C, preferably 140 ° C, still preferably less than or equal to 130 ° C is suitable. Complementarily, the temperature Tf is greater than 120 ° C, to prevent the change of state is completely carried out while the electronic module 14 has not yet reached temperatures that could compromise its operation.

The following fuels are also known, with their vaporization temperature Tv in parentheses: JetB and JP4 (80 ° C), AvGas and AutGas (60 ° C).

For these fuels, a temperature Tf lower than 50 ° C is suitable. The integration of the PCM materials into the electronic module can be carried out in different ways, as shown in FIG. 2, which schematize three variants that are not necessarily exclusive of each other.

In a first variant, the electronic components 110 are encapsulated in the material PCM1. For this, a specific matrix comprising PCM material is used. This variant requires that the electronic components 110 be sealed.

In a second variant, the PCM2 material may be integrated in the substrate 100. US2013 / 0147050 discloses such integration in the substrate 100. A specific volume must then be arranged in the substrate 100.

In a third variant, a cold plate 120 is provided against the substrate 110, on the opposite side to the electronic components 110. The cold plate 120 is therefore positioned between the heat exchanger 16 and the base substrate 100. The cold plate 120 has in order to promote the cooling of the electronic module 14. The PCM3 material is then integrated with this cold plate 120.

These three variants can be combined without difficulty.

Different types of exchangers have been described previously. Depending on the type of exchanger, the relative positioning of the fuel circuit and the base substrate and / or the cold plate can be adapted. In particular, the heat exchanger can be housed in the base substrate 100 or in the cold plate 120. The exchanger can then take the form of a fluid circuit, such as a branch of pipe, arranged in the plate. The circulation of the fluid is then preferably forced by a dedicated pump.

The PCM material may comprise hydrated salts, paraffins, and / or alcohols. The advantage of PCM materials also lies in the gain in mass and volume compared to other technologies.

In a particular embodiment, the electronic module 14 is a power module, configured to convert the energy supplied by the energy source. It is therefore particularly subject to temperature rises, particularly during very short periods during which it is requested.

In this embodiment, the electronic components 110 may in particular be power semiconductors. At present, a more global architecture in the context of a helicopter will be described. Nevertheless, the invention is implemented on any aircraft comprising electronics generating heat, regardless of the number of engines or their type.

FIG. 4 illustrates a rotary wing aircraft 1, more specifically a helicopter with a main rotor 2 and an anti-torque tail rotor 3 coupled to a power unit 4 for their actuation. The illustrated engine group 4 comprises a first heat engine 5a and a second heat engine 5b. These heat engines 5a, 5b are turbine engines and more specifically turbine engines whose power take-off shafts 6 are both connected to a main gearbox 7 to actuate the main rotor 2 and the tail rotor 3.

The motor unit 4 is illustrated in greater detail in FIG. 5. Each heat engine 5a, 5b comprises a compressor 8, a combustion chamber 9, a first turbine 10 connected by a rotary shaft 11 to the compressor 8 and a second turbine 12 , or free turbine, coupled to the power take-off shaft 6. The compressor assembly 8, combustion chamber 9, first turbine 10 and rotary shaft 11 is also known as a "gas generator". The rotary shaft 11 of each gas generator is mechanically coupled to the energy source 13a, 13b, which is more precisely an electric machine 13a, 13b generally in the form of a motor-generator, electrically connected to the electric module 14a , 14b, which is here an electronic power module, which is more specifically a power converter also electrically connected to an electrical storage device 20 and to an electrical network of the aircraft 1. This electrical storage device 20 may for example be a battery, although other electrical storage devices (eg fuel cells or flywheels) are also possible.

The electric machines 13a, 13b serve both for starting the corresponding heat engines 5a, 5b and for generating electricity after this start. In the first case, the electric machine 13a, 13b operates in motor mode, and the power electronics module 14a, 14b provides its power supply from the aircraft electrical network and / or the electrical storage device 20. In the second case, the electrical machine 13a, 13b operates in generator mode, and the power electronics module 14a, 14b adapts the generated current to a voltage and amperage suitable for supplying the electrical network of the aircraft and / or the electrical storage device 20.

Furthermore, however, each electric machine 13a, 13b can also serve to maintain the corresponding heat engine 5a, 5b in standby mode, even during the flight of the aircraft 1, by rotating its rotary shaft 11, with the chamber of combustion 9 extinguished, at a reduced speed Nveille, which can be, for example, between 5 and 20% of a nominal speed NI of the rotary shaft 11. In fact, it is known that the maintenance of a heat engine to turbine in standby mode on a multi-engine aircraft saves fuel in cruising flight and accelerate its eventual restart.

The power supplied by the power unit 4 can vary substantially according to the flight step of the aircraft 1. Thus, the power required for the cruising speed is normally substantially lower than the maximum continuous power of the power unit 4, and even less in relation to its maximum takeoff power. However, the engine group 4 being dimensioned according to the latter, it is substantially oversized compared to the power required for the cruising speed. Consequently, when cruising, with the two thermal engines 5a, 5b in operation, they could find themselves away from their optimal operating regime, which would result in a relatively high specific consumption. In principle, with a motor unit comprising a plurality of heat engines, it is conceivable to maintain the cruising speed with at least one of these engines extinguished. With other thermal engines operating at a speed then closer to their optimal regime, the specific consumption can be reduced. In order to allow such a mode of operation of a power unit, while ensuring the immediate start of the engine off, it has been proposed in FR 2 967 132 to keep the engine off in standby mode.

In the engine group 4 illustrated in FIG. 5, the first heat engine 5a is thus extinguished during the cruising speed of the aircraft 1, while the second heat engine 5b supplies all the power to the main rotor 2 and to the tail rotor 3 through the main gearbox 7. The electric machine 13b associated with the second heat engine 5b simultaneously provides power to the electrical network of the aircraft 1 through its power electronics module 14b and the power supply of the machine 13a through its electronic 14a. In order to be able to ensure the emergency start of the first heat engine 5a, in particular in case of failure of the second heat engine 5b, the first heat engine 5a is maintained in standby mode by actuating its rotary shaft 11 by the corresponding electric machine 13a , powered through its power electronics module 14a.

To supply the heat engines 5a, 5b with fuel, each is associated with the fuel supply circuits 15a, 15b, with the heat exchanger 16a, 16b and, in addition, a fuel filter 17a, 17b located downstream of the heat exchanger 16a, 16b in the direction of the flow of fuel to the engine 5a, 5b.

As illustrated in FIG. 3, each heat exchanger 16a, 16b is adjacent to a base of the power electronics module 14a, 14b (for example a cold plate 21) corresponding, in a housing 22, which can be sealed and common to the power electronics module 14a, 14b and the heat exchanger 16a, 16b corresponding, so that the fuel flowing through the heat exchanger 16a or 16b can be heated by heat generated by the operation of the power electronics module 14a, 14b, and simultaneously contribute to the cooling of the power electronics module 14a, 14b to enable it to operate in an optimum temperature range. Typically, each power electronics module 14a, 14b can process a power Pe of the order of 100 kW, with thermal losses of less than 10%, thus resulting in a caloric power Ph of, for example, less than 10. kW, or even less than 1 kW.

However, each power electronics module 14a, 14b may have a normal operating mode and a degraded electrical performance operating mode that can be implemented to generate additional heat for heating the fuel. This degraded efficiency mode of operation can be obtained for example by imposing on semiconductors of the power electronics module 14a, 14b a cutting frequency higher than that which would normally be applied according to the usual electrical dimensioning criteria.

Each fuel supply circuit 15a, 15b may also comprise a bypass duct 18a, 18b of the heat exchanger 16a, 16b, and a three-way valve 19a, 19b for controlling the flow of fuel through the fuel. heat exchanger 16a, 16b or by the bypass duct 18a, 18b.

To heat the fuel supplying one of the heat engines 5a, 5b during a starting thereof at low temperature before igniting the combustion chamber 9, the latter is directed through the corresponding heat exchanger 16a, 16b, in which it is heated by the heat generated by the operation of the power electronics module 14a, 14b through which the electric machine 13a, 13b is electrically powered to rotate the rotary shaft 11 of the engine 5a, 5b. If the heat generated by the power electronics module 14a, 14b in normal operating mode is insufficient to allow a quick start without risk of clogging of the fuel filter 17a, 17b by water ice particles, a mode of degraded electrical performance operation of the power electronics module 14a, 14b can be implemented to increase the heat generation in this module, and its transmission, through the heat exchanger 16a, 16b, to the fuel.

On the other hand, if it is not necessary to heat the fuel for one or other of the heat engines 5a, 5b, or to cool the associated electronic power module 14a, 14b, the three-way valve 19a, 19b can direct the fuel through the corresponding bypass duct 18a, 18b.

Claims (12)

claims An assembly comprising: a fuel supply circuit (15, 15a, 15b) configured to supply a fuel turbine engine, An electronic module (14, 14a, 14b), A power source (13, 13a) , 13b) for supplying the electronic module (14, 14a, 14b) with electricity, a heat exchanger (16, 16a, 16b) positioned to allow a heat flow of the electronic module (14, 14a, 14b) to the electronic circuit fuel supply (15, 15a, 15b), the assembly being characterized in that the electronic module (14, 14a, 14b) comprises a phase change material (PCM), configured to change state when its temperature reaches a predetermined phase change temperature (Tf). 2. An assembly according to the preceding claim wherein said predetermined phase change temperature (Tf) is lower than the vaporization temperature of the fuel (Tv). An assembly according to any one of the preceding claims, wherein the electronic module (14, 14a, 14b) is an electronic power module configured to convert energy supplied by the power source (13, 13a, 13b). ). An assembly according to any one of the preceding claims, wherein the phase change temperature (Tf) is less than 150 ° C, preferably less than 140 ° C. 5. An assembly according to any one of the preceding claims, wherein the electronic module (14, 14a, 14b) comprises the following elements: - a base substrate (100) forming a support, - electronic components (110), positioned on the support, and wherein the exchanger (16, 16a, 16b) is located, relative to the base substrate (100), on the opposite side of the components (110). The assembly of claim 5, wherein the electronic components (110) are encapsulated in phase change material (PCM). The assembly of claim 5 or 6, wherein phase change material (PCM) is integrated with the base substrate (100). 8. The assembly of claim 5 or 6 or 7, wherein the electronic module (14, 14a, 14b) comprises a cold plate (120) and wherein phase change material (PCM) is integrated with the cold plate. A power plant (4) comprising: A turbine engine (5a, 5b), an assembly according to any one of the preceding claims, wherein the fuel supply circuit (15, 15a, 15b) is configured to supplying the heat engine (5a, 5b). 10. Motor unit (4) according to the preceding claim, wherein the energy source is an electric machine (13, 13a, 13b) operable as a motor or generator and wherein the electric machine is mechanically coupled to a rotating shaft. of the engine. 11. A method of heating fuel using an assembly according to any one of claims 1 to 8 or a power unit according to any one of claims 9 to 10, wherein the fuel is heated, in the heat exchanger (16, 16a, 16b) of the fuel supply circuit (15, 15a, 15b) by the heat emitted by the electronic module (14) through the phase change material (PCM). 12. Use of phase change material (PCM) for controlling heat transfer between an electronic module (14) generating heat when energized, and secondly a turbine fuel gas, through a heat exchanger.